Emergency stop devices are devices that help ensure safe working conditions for personnel working in and around machinery. Such machinery may exist, for example, in factory settings, manufacturing settings, agricultural settings, foundry settings, warehouse settings, or other industrial settings. Often, the machinery (e.g., industrial presses, die machines, milling machines, molding machines, robotics, conveyor belts, etc.) may include moving parts or other hazards that can be dangerous to the personnel working around the machinery. In the event of a dangerous situation where the safety of a worker may need to be maintained, an emergency stop device can be actuated to immediately cease operation of the particular machine. By providing one or more emergency stop devices within quick reach of workers, injury can be avoided or mitigated.
One commonly used emergency stop device is a cable pull switch (also called a grab wire switch, a safety rope switch, or other similar names). A cable pull switch is coupled to one or both ends of a relatively inelastic cable (e.g., a steel cable). When properly installed, pull cable exerts a tension on the cable pull switch. So configured, a long distance (e.g., 100 meter or more) of pull cable can provide a nearly continuous emergency stop function that is easily activated around machinery or along conveyor belts. Any notable deflection or force exerted on the pull cable (e.g., by a worker pulling on the pull cable) can trigger the cable pull switch to effect an emergency stop of the machinery or equipment to which it is connected.
Existing cable pull switches utilize mechanical contact blocks with binary on/off or open/closed states. These existing cable pull switches act like a snap action switch where a transition between an on and off state occurs almost instantaneously in reaction to the worker pulling the pull cable. When a worker pulls the pull cable, a portion of the pull cable is deflected, which results in a linear displacement of the end of the pull cable coupled to the cable pull switch. When the linear deflection at the cable pull switch exceeds a threshold, the contact blocks become activated (e.g., with snap action) and the emergency stop is implemented. Additionally, many cable pull switches protect against pull cable failure by implementing an emergency stop if the pull cable enters a slack condition (e.g., not enough tension exerted by the pull cable on the switch) or a cut condition (no tension on the cable and none at the switch). To implement this, existing pull switches may have a second mechanical contact block that becomes activated when the linear displacement of the end of the cable connected to the pull cable is reduced by action of a tensioning spring within the cable pull switch as the cable enters the slack or cut condition, or utilize an unstable system where too much or too little tension causes a mechanism to actuate the contact block.
The linear physical positions of the activation points of the contact blocks and mechanism dictate the thresholds of operation of the cable pull switch. These thresholds are not easily altered, and therefore require careful adjustment of the tension of the pull cable during operation and repeated checks and adjustments over the lifetime of the pull cable installation (for example, as the cable stretches to generate slack or as the temperature changes in a particular application setting). Existing cable pull switches utilize a mark on the movable portion of the cable pull switch (e.g., a shaft connected to the pull cable), which is then compared to a mark on the cable pull switch body to determine if a length of the pull cable is adjusted such that the proper tension is exerted on the pull cable by the cable pull switch. The tension of the pull cable is often adjusted with one or more turnbuckles or with a cable tensioning system. Though suitable for at least some purposes, such approaches do not necessarily meet all needs of all application settings and/or all users. For example, a technician installing or adjusting the tension on the pull cable may have to adjust elements that are located a distance from the cable pull switch (e.g., 25 meters or more), in which case the technician (e.g., if working alone) would have to iteratively walk between the adjustment location and the cable pull switch to properly adjust the tension.
Further, because the positions of the activation points of the contact blocks dictate the thresholds of operation of the cable pull switch, tension on the pull cable may have to be adjusted more often to account for thermal expansion/contraction. The thresholds are often fairly close together to allow for easy detection of a pull on the cable, thereby creating a safer environment. However, the close threshold may create a false trigger situation if the pull cable were to expand or contact due to thermal changes.
Additionally, present cable pull switches are susceptible to jamming or other conditions rendering the cable pull switch incapable of registering a cable pull event. For example, a shaft of the cable pull switch may become deformed or damaged or the cable may become pinched. Present systems are unable to detect a jamming situation until a user pulls on the cable. Accordingly, technicians or other maintenance crew are required to perform routine checking of pull cable systems to ensure proper operation and to ensure that a previously undetected physical deformity in the cable pull system has not rendered the system inoperable.
Additionally, existing cable pull switches are binary in operation, both in their output signal and in their method of detection. Accordingly, existing cable pull switches lack a dynamic response to environmental and situational changes and are therefore limited in their flexibility and application.